Nanoscale physics

The effect of low-energy Ar+ ion irradiation parameters on the structure and properties of Ni/Cu/Cr thin films
I.O. Kruhlov, L.M. Kapitanchuk, S.I. Sidorenko, S.M. Voloshko

Metal Physics Department, National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Prospect Peremogy 37, 03056 Kyiv, Ukraine
E-mail: kruhlov@kpm.kpi.ua

Low-energy ion irradiation of thin metal films is an effective approach for modifying their structure and physico-chemical properties [1]. In this study, the influence of such parameters as irradiation energy (400-1400 eV), ion beam current density (4-8.5 mkA/cm2) and treatment duration (20-40 minutes) on the development of oxidation-reduction processes, impurity and structural effects is investigated in layered Ni/Cu/Cr films. Modification of the films under various ion bombardment parameters was studied by synchrotron radiation X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and scanning electron microscopy (SEM). It is established, that the competition of re-deposition and sputtering of surface atoms determines the final properties, depending on the ionic current density. Re-deposition processes predominate when the lowest current density of 4 mkA/cm2 is applied, even in case of the longest exposure, causing the formation of a non-conductive amorphous layer on the surface. In that case, the intensities from Ni, O and C lines on XPS scans decreases so much, that determination of the surface phase composition becomes much challenging. Simultaneously, the saturation of the stack by impurities is observed, which significantly reduces the crystal structure perfection of Cu layer. However, when the ion current density is increased to 8.5 mkA/cm2, the surface sputtering processes become dominant. As a result, the content of impurities, especially O, through the film depth is decreased due to the reduction of oxidized sublayers at the interfaces and grain boundaries. The crystal structure perfection of the Cu improves significantly compared to the as-deposited state due to the ion-induced long-range effects. However, according to SEM data, increasing the beam energy to 1000 eV with a current density of 8.5 mkA/cm2 causes the formation of macrodefects clusters on the surface, which can negatively affect the functional and technological properties of the studied thin films.

1. Kruhlov I.O., Vladymyrskyi I.A., Dubikovskyi O., Sidorenko S.I., Ebisu T., Kato K., Sakata O., Ishikawa T., Iguchi Y., Langer G.A., Erdélyi Z., Voloshko S.M. Oxidation and reduction processes in Ni/Cu/Cr/Si(100) thin films under low-energy ion irradiation // Mater. Res. Express.-2019.-6.- 126431.